Blowout preventers are used to maintain control of wells during drilling. Ram-type blowout preventers are used to close on the drill or pipe string to contain pressure in the well. At times it is necessary to strip or move the string through the closed rams. This stripping movement can severely wear or abrade the face of the resilient packers used in blowout preventer rams. Another reason the packers of ram-type blowout preventers are subject to wear is that to provide a seal they must tightly engage and conform to the irregular surface of the string when closed and such ability to conform causes the packers to be subject to pressure induced extrusion. The design of ram packers is thus a compromise to provide the needed conformity or feed of the resilient material with maximum abrasion and extrusion resistance.
Examples of prior ram-type blowout preventers can be seen in U.S. Pat. Nos. 2,883,141 and 3,692,316 which disclose the use of upper and lower packer plates designed to minimize extrusion damage. U.S. Pat. No. 4,323,256 discloses the use of a polytetrafluoroethylene insert in the face of the packer to minimize wear in stripping of the string through the packer. U.S. Pat. No. 2,194,258 discloses a ram-type blowout preventer having upper and lower plates of the packer which include a series of strips which are generally parallel to the ram axis and can move independently of each other to engage a drill or pipe string on which the rams have closed to provide a uniform support for the resilient packing material.